Impression trays are used by dentists for purposes of making impressions of the teeth and adjacent tissue so that custom-made prosthetics and appliances can be made for a patient such as for restorative dental work or orthodontic treatment. The steps included for making the impression include the loading of an impression tray with impression material sufficient to obtain the desired impression and then taking the impression by inserting the tray/impression material into the mouth of a patent and having it engage the teeth and tissue for which an impression is desired. The impression material is allowed to set and then the tray/impression material is removed from the patient's mouth followed by a recording of that impression such as by pouring and curing a suitable plaster or stone in the impression. If during the removal of the tray/impression material from the mouth of a patient the impression material becomes substantially disengaged from the tray the impression taken may be sufficiently destroyed or distorted thereby necessitating the taking of a further impression.
Various devices have been heretofore developed for assisting in the retention of impression material in the impression tray to inhibit separation of the impression material from the tray during the removal of the tray/impression material from the mouth of a patient. These devices have included perforations or apertures in the form of round holes and wires as in U.S. Pat. No. 2,963,786; extending arms terminating in ball-shaped ends as in U.S. Pat. No. 3,686,759; enlarged flanged edges and ribs as seen in U.S. Pat. No. 3,834,025; a plurality of slits as seen in U.S. Pat. No. 4,146,963; upwardly extending ball-shaped members as seen in U.S. Pat. No. 4,227,877; undercuts as seen in U.S. Pat. No. 4,368,040; and non-woven fabric bonded to the surface receiving the impression material as seen in U.S. Pat. No. 4,530,662. Various other methods of retention have also been used, many of which have resulted in presenting difficulty in cleaning the trays for future use once the impression has been recorded.